1. Field of the Invention
The present invention relates to an integral-type hydraulic and mechanical transaxle apparatus for driving and steering a vehicle comprising a single housing in which a pair of driving axles, a differential mechanism for differentially connecting both the driving axles to each other, two driving and steering hydraulic stepless transmissions (xe2x80x9cHSTsxe2x80x9d hereinafter) each of which fluidly connects a hydraulic pump and a hydraulic motor, and a mechanical transmission for transmitting outputs of both the hydraulic stepless transmissions to the differential mechanism are accommodated.
2. Related Art
Conventionally, there is a known transaxle structure as disclosed in U.S. Pat. No. 4,782,650 and Japanese Patent Application Laid-open No. H2-261952 for example, in which in order to drive a pair of left and right driving axles for driving a vehicle or a crawler sprocket, and in order to steer both the axles at different driving speeds, one HST for each of the axles, i.e., total two HSTs are used. The two HSTs are arranged such that both output rotational speeds are uniform when the vehicle runs straight, the output rotational speeds are different when the vehicle is steered.
In this conventional mechanism, the output rotational speeds between both the HSTs must be uniformed strictly, and if capacities of both the HSTs are different, turning movement becomes different between a right-hand turn and a left-hand turn. Further, the HSTs for pivotally supporting the axles are provided side-by-side on axes of both left and right axles (i.e., the two HSTs are arranged on the left and the right, side-by-side at central portions in the lateral direction of the vehicle, and both of the axles are extended to the outer sides of the two HSTs in the lateral direction of the vehicle). Therefore, the width of the vehicle is increased and installation space of the HSTs is also limited. If the vehicle width is increased, it is disadvantageous for a vehicle used for operation that requires sharp turning movement.
For this reason, there are increasing tendencies to develop a structure for driving and steering axles in which a pair of axles are connected to each other through a differential mechanism, two HSTs having different functions are provided, and the output of both the HSTs is transmitted to the differential mechanism One of the HSTs (HST for driving operation) is connected to a speed-change operation member such as a lever or pedal provided in the vehicle for rotating both the axles forward and backward, and for steplessly changing the rotational speed based on the operation of the speed-change operation member. The other HST (HST for steering operation) is associatively connected to a steering operation member such as a steering wheel or the like provided in the vehicle for producing different rotational speeds between both the axles based on the steering direction and steering amount of the steering operation member.
In the case of this structure, both the axles are basically driven based on output of the one driving HST, whereby strict factory-operation to uniform the output of two HSTs for ensuring the straight traveling performance is not required unlike the conventional structure. Further, the rotational speeds of both the axles can be changed from each other for steering operation based on the output of the one steering HST. Therefore, unlike the conventional structure, there is no inconvenience that turning radius ratio with respect to the steering angle is changed between the left-hand turning and the right-hand turning due to the difference in capacities between the two HSTs.
Further, both the HSTs need not be arranged side-by-side in the axial direction of the axles, and the HSTs can be disposed in positions that deviate longitudinally from both the axles. Therefore, the vehicle width can be reduced, and this is advantageously applied to a vehicle requiring a sharp turning operation. Further, the flexibility in the layout of the HSTs is excellent.
There are increasing tendencies to develop inventions in which based on such a transaxle structure, a mechanical transmission (drive train) for connecting the output sections of both HSTs with a differential mechanism is accommodated together with both the HSTs in a single housing which accommodates both the axles and the differential mechanism, thereby forming a compact integral-type transaxle apparatus.
There is also a known structure in which a differential mechanism comprises a pair of planetary gear mechanisms and is formed compact, both the output of a driving HST and the output of a steering HST are transmitted to planetary gears of each of the planetary gear mechanisms, and the axle is rotated by revolution of the planetary gear.
However, in the known integral-type transaxle apparatus accommodating all the constituent elements in such a single housing, a pump shaft and a motor shaft of each of the HSTs are in parallel to each other (e.g., both are directed in vertical direction). When the above structure is applied to a lawn mower tractor and the like using an engine whose output shaft is directed in the vertical direction, it is preferable that the pump shaft also serving as an output shaft is directed in the vertical direction. However with this layout, the motor shaft is also directed in the vertical direction. On the other hand, when a gear is used as the input means of the differential mechanism, the axis of the gear is directed in the horizontal direction because of its structure. Therefore, in the mechanical transmission, when a gear train is structured as a drive train from the vertical motor shaft to the differential mechanism, a gear provided on the vertical motor shaft and an input gear of the differential mechanism are twisted with respect to each other, a bevel gear must be provided therebetween and its structure becomes complicated, and installation space must be increased. Further, when the motor shaft is directed in the vertical direction, a hydraulic motor is disposed above or below a center section. Therefore, if a gear train from the motor shaft is structured, the gear train must be disposed in the opposite side from the hydraulic motor shaft with respect to the center section, and the housing must be increased in the vertical direction correspondingly.
Thus, the integral-type transaxle apparatus has a room for further reducing its size.
It is an object of the present invention to provide an integral-type hydraulic and mechanical transaxle apparatus for driving and steering a vehicle, comprising a single housing accommodating a pair of driving axles, a differential mechanism for differentially connecting both the driving axles, a driving HST and a steering HST, each of the HSTs fluidly connecting a hydraulic pump and a hydraulic motor, and a mechanical transmission for transmitting output of both the HSTs to the differential mechanism, in which structure of the HSTs is devised to reduce a size of the apparatus.
To achieve the above object, in the present invention, at least one of the HSTs is disposed such that a rotational axis of a pump shaft and a rotational axis of a motor shaft are perpendicular to each other. Further, the HST includes a center section which allows such an arrangement of the pump shaft and the motor shaft.
Further, in the HST having the rotational axis of the pump shaft and the rotational axis of the motor shaft perpendicular to each other, a rotational axis of the motor shaft of at least one of the HSTs is disposed horizontally.
With the above structure of the invention, the mechanical transmission formed between the output means of the HST mounted to the motor shaft having the horizontal rotational axis and the input means of the differential mechanism having the (horizontal) rotational axis parallel to both the axles for differentially connecting both the axles requires no change of the power transmitting direction by a bevel gear or the like halfway. Further, there are effects that the rotational axis may be kept horizontal as it is, the structure is simple, the number of parts is reduced, the apparatus is compact and the cost can be cut down.
Further, in the present invention, at least one of the motor shafts having horizontal rotational axis is disposed in parallel to the driving axle. With this structure, the motor shaft is extended in the lateral direction, and the longitudinal length of the apparatus can be shortened.
Further, the motor shaft disposed in parallel to the driving axle is provided with an output member and is directly connected to an input member of the differential mechanism for driving the latter. With this arrangement, it is possible to provide the integral-type transaxle apparatus in which the structure of the mechanical transmission from the motor shaft to the input member of the differential mechanism becomes extremely simple, the number of parts is reduced, the motor shaft can be disposed near the input member of the differential mechanism, the size is compact, and the number of parts is reduced, and the cost can be cut down.
Further, if a center section having substantially a d-shape as seen from the side is used as the center section of the HST having the pump shaft and the motor shaft whose rotational axes are perpendicular to each other, the hydraulic pump and the hydraulic motor whose rotational axes are perpendicular to each other can be disposed side-by-side close to each other. That is, in the HST having the motor shaft including a horizontal rotational axis, if the center section having substantially a d-shape as seen from above is disposed in a state in which the hydraulic pump-mounting face is disposed horizontally and the hydraulic motor-mounting face is disposed vertically, the hydraulic pump and the hydraulic motor can be disposed side-by-side close to each other in the horizontal direction, and there are effects that the HST can be formed compactly, and a compact integral type transaxle apparatus can be formed.
Further, the housing is divided into at least two chambers, where both the HSTs are disposed in at least one chamber, and the differential mechanism and the mechanical transmission are disposed in the chamber other than the at least one chamber in which both the HSTs are disposed. With this structure, impurities such as metal chippings generated from the mechanical transmission or the differential mechanism are prevented from entering into the chamber in which the HSTs are disposed, and the durability of the HSTs can be enhanced.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.